File – This Oct. 22, 2010, file photo, shows low water levels in Boulder Harbor in Lake Mead, Ariz. Drought in the southwestern U.S. is depleting the vast Lake Mead on the Colorado River to levels not seen since Hoover Dam was completed and the reservoir was filled in the 1930s. (AP Photo/The Arizona Republic, Mark Henle, file)

LAS VEGAS — Drought in the southwestern U.S. will deplete the vast Lake Mead this week to levels not seen since Hoover Dam was completed and the reservoir on the Colorado River was filled in the 1930s, federal water managers said Tuesday.

The projected lake level of about 1,080 feet above sea level will be below the level of about 1,082 feet recorded in November 2010 and the 1,083-foot mark measured in April 1956 during another sustained drought.

But U.S. Bureau of Reclamation regional chief Terry Fulp said water obligations will be met at least through next year without a key shortage declaration. The result will be full deliveries to cities, states, farms and Indian tribes in an area that’s home to some 40 million people and the cities of Las Vegas, Phoenix and Los Angeles.

“We continue to closely monitor the projections of declining lake levels and are working with stakeholders throughout the Lower Basin to keep as much water in Lake Mead as we can through various storage and conservation efforts,” Fulp said in a statement.

The lake on Tuesday was just under 1,082 feet above sea level, and the reservoir was about 39 percent full, said Rose Davis, a bureau spokeswoman in Boulder City, Nevada.

The dropping level since the reservoir was last full in 1998, at just under 1,296 feet above sea level, has left as much as 130 feet of distinctive white mineral “bathtub ring” on hard rock surfaces surrounding the lake.

Davis said the bureau expects a slight increase in water level to about 1,083 feet by Jan. 1, 2015.

Lake Mead National Recreation Area, 30 miles east of Las Vegas, is among the federal government’s top tourist attractions. It drew some 6.3 million visitors in 2013, about the same number as the Lincoln Memorial in Washington, D.C.

Boaters and swimmers have largely ignored the dropping water levels in a place where splashing in cold fresh water on 100-plus-degree summer days is a treat. But they’ve also dealt with marina closures in recent years. Visitors who used to feed scraps to carp from restaurant deck tables may now need to trek hundreds of yards with sandwiches and beach blankets to enjoy a waterside lunch.

“We projected this was coming,” Davis said. “We are basically where we expected to be, given the dry winters in 2012 and 2013.”

Lake Mead today stores about 10.2 million acre-feet of water and is managed in conjunction with Lake Powell, the reservoir farther up the Colorado River near the Utah-Arizona state line.

Davis said Lake Powell was at 52 percent capacity, holding about 12.7 million acre-feet of water.

Water officials say an acre-foot is about enough water to supply an average Nevada household for a year.

Fulp compares controlled management of the two largest reservoirs on the Colorado River to pouring tea from one cup to another.

Seven southwestern U.S. states reap the result under a 1928 allocation agreement that also provides shares of Colorado River water to Native American tribes and Mexico.

Las Vegas, with more than 2 million residents and about 40 million tourists a year, is almost completely dependent on Lake Mead for drinking water.

Federal and state water officials have negotiated plans for a shortage declaration triggering delivery cuts to Nevada and Arizona if annual projections for the Lake Mead water level drop below a 1,075 foot elevation. That projection is based on data being compiled by the Bureau of Reclamation.

Davis said the 1,075-foot trigger point is not expected this year or next. But last year, after back-to-back driest years in a century, federal water managers gave Arizona and Nevada a 50-50 chance of having water deliveries cut in 2016.

California, Colorado, Utah, New Mexico and Wyoming wouldn’t see direct cuts in their share of river water, but officials have acknowledged there would be ripple effects.

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